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| | Abstract | | The records of the Yamagata-oki earthquake on June 18, 2019, obtained at the Kashiwazaki-Kariwa Nuclear Power Station, were analyzed with an awareness of spatial variations. Although there are folds in the geological structure of the site, the Fourier spectrum of the records obtained at the observation points deployed in the site was stable with little fluctuation at frequencies below 0.5 Hz. However, when investigating the propagation characteristics of waves in the time domain using a low-pass filter waveform with a frequency of 0.2 Hz or less, the apparent propagation speed and direction differed depending on the time and the location in the site. To investigate the spatial variation, the f-k spectrum analysis was performed on the entire site, the syncline in the southern part of the site, and the anticline in the northern part of the site. The velocity and direction of arrival obtained for each frequency varied widely, but there was a tendency consistent with the previous knowledge of underground structures. |
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